It is a common practice in agricultural practice to apply herbicidal compositions to control undesirable vegetation in cultivated crops. Such herbicidal compositions may contain other additaments such as fertilizers, biocides, e.g., insecticides, fungicides, nematicides, etc., herbicide antidotes, etc.
Additional agricultural practices include the application of said herbicidal compositions to soils or vegetation previously treated with said biocides. However, a long history of experience with focused attention developing in the early 1960s has shown that major problems can arise as a result of the interaction of herbicides and various biocides, particularly various insecticides and/or fungicides. The common result of such interaction is the enhancement of the phytoxic activity of the herbicide in various crops. This enhanced phytotoxicity is referred to in the literature and will be so used herein as "negative synergy/synergism" between the herbicide(s) and the biocide(s). Such negative synergism is expressed in terms of decreased emergence of a crop, reduced crop survival or vigor, crop stand reduction and/or crop yield.
The herbicides and biocides giving rise to negative synergy when in contact with each other have been found to include members from a variety of classes, including, but not limited to, in the case of herbicides, sulfonylureas, imidazolinones, aliphatic and aromatic carboxylic acids, amides salts and esters, isoxazolidinones, ureas, triazines, thiocarbamates, acetanilides, etc., etc. In the case of insecticides, organic phosphates ("organophosphates" or "OPs"), carbamates, pyrethroids, cyclopropanecarboxylic acid esters, carboxamides, dicarboximides, perchlorocyclohane, etc.
Negative synergism has been found to occur between herbicides and insecticides in a variety of crops including small grain crops, narrow leaf crops, e.g., corn, rice, barley, sorghum, wheat and broadleaf crops such as cotton, soybeans and sugarbeets.
Illustrative examples of the phenomenon of negative synergism from the literature are plentiful and readily available and typical ones are cited here. For example, Walter et al, Texas Agricultural Experiment Station Progress Report 2284 (1963) and J. Hacskaylo et al Weeds 2:88-291 (1964) reported injury to cotton seedlings following use of combinations of monuron or diuron herbicides and phorate (also known as thimet) or disulfoton systemic insecticides. Schweizer and Ranney reported on interactions among EPTC plus diuron and trifluralin herbicides and captan-terrachlor fungicide and phorate on cotton. Mississippi Agr. Exp. Sta. Information Sheet 877 (1965).
A series of studies in 1966-1969 by A. Y. Chambers et al reported in Proc. SWSS, 21:54-66 (1966) and 83-92 (1969) and Tennessee Farm and Home Science, 66:13-15 (1968), summarized work initiated at the University of Tennessee West Tennessee Experiment Station to evaluate cotton herbicides for interactions when applied with soil fungicides and systemic insecticides. The studies reported by Chambers et al involved a variety of types of pesticides, including as herbicides fluometuron, diuron and norea ureas; CIPC (a carbamate); DCPA (a terephthalate); prometryne (a triazine); trifluralin (a dinitrotoluidine) and nitralin (an aniline) and as fungicides, captan plus terrachlor plus terrazole and as insecticides, disulfoton with and without phorate. In these studies Chambers et al observed significant interactions between the pesticides, with many combinations of pesticides giving a variety of negative synergistic effects, including reduction in seedling emergence, significant reduced cotton seedling survival and/or vigor and/or stand reduction and/or yield.
Reports by H. W. Ivy et al in Proc. SWSS, p. 94, 1969 and p. 132, 1973 cite a variety of pesticide interactions with the same herbicides used by Chambers et al; chloroneb or PCNB with or without Terrazole fungicides and phorate, disulfoton and UC-21149 (aldecarb) insecticides. Various combinations resulted in negative synergism in cotton.
In Proc. SWSS-95, 1969, B. J. Johnson reported negative synergism in terms of significantly reduced seedling vigor in soybeans due to the interaction of various combinations of Amiben ethyl ester, trifluralin and linuron herbicides and methomyl and phorate insecticides.
R. M. Hayes et al reported that use of non-recommended rates of the herbicide metribuzin and the insecticides disulfoton and phorate resulted in significant reductions in yield and stand reductions of two varieties of soybeans. Proc. SWSS-1976 p. 95.
More recently, C. D. Applewhite reported (Proc. SWSS, p. 83, 1990) on tests in cotton with various application modes (granular in-furrow or tank spray) of clomazone with and without fluometuron herbicides in combination with the OP insecticides disulfoton, phorate, aldecarb and acephate and the nematicide fenamiphos. A number of combinations of these chemicals and application modes gave a variety of responses ranging from the safening of clomazone by the interaction of disulfoton and phorate applied in-furrow as granular formulations, but accompanied by some plant discoloration and a 7% stand reduction; no effect on safening by fenamiphos, but producing the same plant discoloration and stand reduction as the OP insecticides. Applied as in-furrow sprays at various rates, disulfoton safened clomazone, but gave 5% discoloration and stand reduction, whereas without the safening, fenamiphos and acephate gave the same discoloration and stand reduction.
Applewhite further reported that combinations of clomazone alone or with fluometuron applied PPI or PRE at different rates to aldecarb or phorate resulted in no adverse reactions. However, at lower rates aldecarb applied in-furrow failed to reduce cotton discoloration and stand reduction.
In a recent technical bulletin dated Sep. 5, 1990 to its dealers, the proprietary owner of the sulfonylurea herbicide, ACCENT.RTM. (common name "nicosulfuron") cautioned that COUNTER.RTM. soil insecticide (an OP) can react with ACCENT, resulting in damage to corn. Thus, the ACCENT label prohibits the use of that product if COUNTER has been applied as a soil insecticide. The recommendation is to use alternative soil insecticides (but none are specified).
In a similar technical bulletin dated Oct. 23, 1990 to its dealers, the proprietor of BEACON.RTM. (common name "primisulfuron") herbicide, also a sulfonylurea herbicide, stated that: "Extensive field tests and scientific research shows that when COUNTER is present in the corn plant, an application of a sulfonylurea herbicide like BEACON often can cause injury to the corn plant. The chemistry in COUNTER slows the metabolism of the plant, which interferes with the detoxification process . . . we have conducted extensive lab and field tests, independently and in cooperation with American Cyanamid, to discover ways to avoid this negative synergy. We've examined application timing and methods and various Counter formulations--including COUNTER 20 CR--but to date there is no reliable solution to this problem . . . . The Beacon label for 1991 will continue to prohibit use of BEACON whenever COUNTER has been applied . . . growers have other options to control troublesome insects." (Underlines in cited document).
In an article in the Canadian Journal of Plant Science, Vol. 58, pp. 1119-1121 (October, 1978), numerous citations are made to studies resulting in findings of negative synergism between various herbicides and insecticides in various crops, including corn injury by the interaction of Eradicane and fonofos.
In the study reported in said article, the authors evaluated the effect on corn of applications of the insecticide fonofos on the herbicides EPTC and vernolate containing the antidote dichlormid (i.e., Eradicane and Surpass, respectively). In tests in succeeding years (1976 and 1977) the authors found no negative synergy between fonofos and the herbicides containing the antidote in 1976, but in 1977 found severe damage to corn ear quality and reduction in tiller numbers, albeit insignificant, by Eradicane plus fonofos. The 1977 results confirmed reports by some growers in 1975. No negative synergy was found between the Surpass plus fonofos treatments in either of the two-year trials.
The authors concluded that negative synergy with these herbicides and fonofos in corn can be inconsistent from year to year, possibly because of soil and weather conditions. It is noteworthy that the authors did not even discuss, much less recognize, any significance in the presence of the antidote dichlormid--which in their 1977 tests did not prevent corn injury. Nor did the authors comment on the fact that the particular combination of vernolate plus dichlormid caused no injury to corn, with or without fonophos, an inference, therefore, that vernolate and fonophos may not induce negative synergism.
On the other hand, in tests with fonofos and other soil-insecticides, e.g., terbufos, chlorpyrifos and thimet, with another herbicide, the sulfonylurea nicosulfuron (active ingredient in Accent.RTM. herbicide), in corn Drs. H. Wilson at VIP & SU and F. Webb, University of Delaware, found negative synergism in all treatments (in-furrow, T-band, side-band and surface band applications).
It is seen from the literature that various postulates have been advanced to explain the basis for the noted negative synergy between various herbicides and biocides, especially OP systemic insecticides, in various crops. Thus, Hayes et al, supra, point to use of off-recommended rates of the pesticides. The above-mentioned technical bulletin regarding BEACON herbicide points to interruption of plant metabolism leading to detoxification thereof.
A variety of solutions have been proposed to avoid the negative synergy problem. Thus, Chambers et al, supra, concentrated on intensive evaluations of combinations of preemergence herbicides, systemic insecticides and soil fungicides in cotton. Still other proposed solutions to the problem include the avoidance of tank mixing the herbicide and biocide or delaying the application for many days or weeks after the biocide has been applied to the soil. Various workers have proposed formulating the biocide as a controlled release ("CR") formulation. Both of the above technical bulletins concerning ACCENT and BEACON herbicides solve the negative synergy problem by avoiding it, i.e., prohibit use of those herbicides, both sulfonylureas, when the soil insecticide COUNTER, has been used.
It is, therefore, an object of this invention to minimize, reduce or eliminate negative synergy arising from the interaction of herbicides and biocides. Particular embodiments of the invention refer to the use of herbicides which exhibit ALS inhibitory action in weed plants, especially sulfonylurea, imidazolidinones, azolopyrimidine sulfonamides, and the like. However, other herbicides not included in the foregoing classes of compounds have also exhibited negative synergy with biocides, even though such other herbicides, e.g., acetamides, thiocarbamates, etc., are not known to be ALS inhibitors, but do exhibit a similar mode of inhibitory action.